1. Field of the Invention
The invention relates to a multicolor photovoltaic electrochromic apparatus.
2. Description of Related Art
An electrochromic device is a device constituted of conductive materials for performing color change when an electric field or current is applied to cause a reversible redox reaction. An electrochromic device should be fabricated to meet the following requirements: colors of the electrochromic device should be easily recognizable under different potentials; the change of color should be rapid and uniform; reversibility of the color change should be repeatable at least ten thousand times; and the device should have high stability. Commonly-used electrochromic devices include solid-type surface-confined thin-film electrochromic devices and solution-type electrochromic devices.
The structure of a surface-confined thin-film electrochromic device is formed by a top transparent substrate, a bottom transparent substrate, and an electrochromic multi-film disposed therebetween. The electrochromic multi-film has a structure similar to that of a battery and includes at least five coated/plated layers of different functions, which are a transparent conductive layer, an electrochromic layer, an electrolyte layer, an ion storage layer, and a transparent conductive layer. The structure of the solution-type electrochromic device includes a top transparent conductive substrate and a bottom transparent conductive substrate and an electrochromic organic solution is disposed therebetween. The electrode being disposed to have said layers facing each other
To extend the application of electrochromic technology, research which combines photoelectric technology and solar cells has provided diverse directions for development. For instance, building integrated photovoltaic (BIPV) solar cells may be coordinated with electrochromic technology to automatically adjust the color of electrochromic windows, based on indoor and outdoor illumination changes, for reducing indoor heat without any additional power supply. As power saving becomes more and more important, such an application has become a new trend.
Compared to electrochromic device which has been developed for some time, the integration of photovoltaic and electrochromic technologies provides better efficiency in energy saving, for photovoltaic electrochromic device can achieve color change in electrochromic layers without additional power source. At the beginning, photovoltaic electrochromic technology is developed based on the concept of using compound films of a Prussian blue electrochromic thin film and a photosensitive layer-TiO2 for performing color change.
In recent years, such a concept has been further extended to separate the photosensitive layer and the electrochromic layer to the anode and the cathode respectively for constituting a device. This kind of device can be described as having electrochromic materials inserted into dye sensitive solar cells, which has become the most widely-discussed subject in the research of photoelectrochromic technology. The electrochromic material is WO3 and the dye sensitive solar cell mainly utilizes Ruthenium Ru-dye. The photoelectrochromic device is a multi-layer photoelectrochemical device that includes two transparent conductive substrates, a working electrode layer formed of photosensitive material and disposed between the transparent conductive substrates, an electrolyte layer, and an auxiliary electrode layer formed of electrochromic material.
U.S. Pat. No. 6,369,934B1 has disclosed a whole organic multi-layer photoelectrochemical device, for instance. However, to apply such a structure to practical applications, many problems need to be overcome such as the long term stability of the photosensitive layer and the possibility of developing devices having larger sizes.
U.S. Pat. No. 5,384,653 provides a variable transmittance of two glass panels separated from each other, wherein an electrochromic layer stack is disposed at the inner side of the first glass panel in conjunction with an array of photovoltaic cells deposited along an edge of the glass panel, to produce electric power necessary to change the color of the electrochromic layer stack. A battery is placed in parallel fashion to the array of photovoltaic cells to allow the user the ability to manually override the system to a desired transmittance.
Moreover, U.S. Pat. No. 5,377,037 has disclosed a design of combining a solar cell with an electrochromic device to form one single device, which is basically manufactured by using a stacking method to combine monolithic silicon thin-film solar cells with an inorganic electrochromic device on a first conductive glass substrate, and then oppositely bonding the silicon thin-film solar cells with another transparent conductive glass substrate. Between the substrates, a liquid organic electrolyte or a solid inorganic electrolyte layer is disposed. The color contrast of the device is comparatively low, makes it less attractive to apply the device in smart windows.
Electrochromic technology also find application in display devices, Some research is focused on using pixel electrodes of thin-film transistor (TFT) and a common electrode to switch the electrochromic device, as disclosed in U.S. Pat. No. 7,312,914. However, this kind of structure requires additional energy supply.
In addition to the above, a multimedia display which combines electrochromic layers and solar cells has been developed, as in U.S. Pat. No. 7,205,473. However, in this type of display, the electrochromic device and the solar cells are fabricated separately and divided in different areas, which is unfavorable to the trend of enlarging device layout.